docs: def Draw(self, *args, **kwargs):
          """
          Loop over subfiles, draw each, and sum the output into a single
          histogram.
          """
          self.reset()
          output = None
          while self._rollover():
              if output is None:
                  # Make our own copy of the drawn histogram
                  output = self._tree.Draw(*args, **kwargs)
                  if output is not None:
                      output = output.Clone()
                      # Make it memory resident (histograms)
                      if hasattr(output, 'SetDirectory'):
                          output.SetDirectory(0)
              else:
                  newoutput = self._tree.Draw(*args, **kwargs)
                  if newoutput is not None:
                      if isinstance(output, _GraphBase):
                          output.Append(newoutput)
                      else:  # histogram
                          output += newoutput
          return output